The present invention relates to a photo-functional device, particularly to a semiconductor photo-functional device in which a light emitting section and a light receiving section are formed on the same semiconductor substrate.
As a semiconductor device in the field of optoelectronics utilizing the excellent properties of light, there is a semiconductor photo-functional device in which light emitting devices and light receiving devices are integrally formed. This photo-functional device is a device having an all-mesa type structure. A hetero junction phototransistor, composed of P-InGaAsP and N-InP, which serves as a light receiving section, and a doublehetero junction light emitting diode, composed of P-InP, n-InGaAsP, and N-InP, which serves as a light emitting section, are integrated vertically on an n-InP substrate via a buffer using N-InP. The electrodes of the device are formed on the upper surface of the diode and the lower surface of the substrate. The characteristics of differential gain, optical bistablity and optical switching have been obtained by controlling light feedback.
However, since the light emitting section and the light receiving section of the photo-functional device of an all-mesa type are integrated vertically, controlling the amount of light feedback is difficult. Therefore, it was difficult to control the input-output light characteristics. Aligning the position of the electrode on the rear side of a substrate with the mesa section for growing a light emitting section was difficult. In the structure of a device by the prior art, when a device is formed as a two-dimensional array, there exist various problems such as the method of supporting a wafer and heat dissipation when it is put into practical use. There was another undesirable point, namely that the number of layers for epitaxial growth is eight or greater, so that at least twice as many layers must be grown for epitaxy.